Grinding machine for generating an epitrochoidal surface

ABSTRACT

A grinding machine for generating an epitrochoidal surface or the like, including means for generating a true epitrochoid and for providing for the use of a cam while using the generating means for maintaining normalcy and preload of the cam against a cylindrical follower.

United States Patent 1191 1111 3,902,278 Uhtenwoldt et a1. Sept. 2, 1975[54] GRINDING MACHINE FOR GENERATING 3,757,474 9/1973 Pedersen 51/105 RAN EPHTROCHOIDAL SURFACE 3,800,621 4/1974 Hoglund 5l/D1G. 32 3,816,9966/1974 Uhtenwoldt 51/DIG. 32 Inventors: Herbert Rudolph Uhtenwoldt,3,828,481 8/1974 Uhtenwoldt 51/1310. 32

Worcester; Richard Earl Crossman, Leominster both of Mass FOREIGNPATENTS OR APPLICATIONS 1,239,213 4/1967 Germany 51/97 R [73] Ass'gneeiCmcmna" Mllacmn'fleald 1,117,569 6/1968 United Kingdom 51/95 RCorporation, Worcester, Mass.

OTHER PUB ICATI N [22] Filed: Nov. 18,1974 L O S Abrasive Engineering,Newest Trochoid Grinder, [2]] Appl. No.: 524,445 M 22,

Related US. Application Data [63] Continuation Of 561. No. 349,924,April 11, 1973, W 'F dbandcmed- Assistant Examzner-N1cho1as P. Gd1c1Attorney, Agent, or Firm-Norman S. Blodgett; Gerry 52 us. (:1. 51/50 PC;51/95 WH; 51/101 R; Blodgett SI/DIG. 32; 82/13; 90/20 [51] Int. Cl B24b/16; B24b 19/08 57 BS C [58] Field of Search 51/50 R, 50 PC, 95 WH,

5l/97 NC 105 R 105 EC 101 R 16593 A grlndmg machme for generatmg anep1trocho1dal DIG 82/1 surface or the like, includlng means forgenerating a true epitrochoid and for providing for the use of a camReferences Cited While using the generating means for maintainingnormalcy and preload of the cam against a cylindrical fol- UNITED STATESPATENTS lowen 2,428,971 /1947 Hauser 51/50 R 3,730,052 5 1973 Harlin 907 Clams, 21 Drawlng Flgures 1| 1 I I 11 1 J 1 1 V 1 I 1 1,1 1 I 1 20I111 L l 12,111 I //----"J I o 29" j 7 F111 5 f 1 l3 PATENTEDSEP 2197s 3902,278

SHEET 3 GE NERATE TRUE EP/TROCHOID COMPENSATE F OR NON-NORMAL! TY VARYSHAPE DE SIRE D SHAPE POINT P MINOR CIRCLE EPITROCHOID FIG 4 BASE CIRCLEFIG. 3

&

SHEET PATENTEU SE? 975 SHEET SHEET PATENTED SEP 2 I975 FIG. I0

FIG. II

PATENTEDSEP 2197s SHEET LAL GRINDING MACHINE FOR GENERATING ANEPITROCI-IOIDAL SURFACE BACKGROUND OF THE INVENTION This is acontinuation of application Ser. No. 349,924 filed Apr. 1 l, 1973. nowabandoned.

The manufacture of grinding machines for the production of non-circularsurfaces is a highly developed art and considerable interest has beenapplied to the generation of the internal epitrochoidal surface which isused in the housing of a Wankel engine. There are two basic principlesemployed for machining an epitrochoidal surface, (a) cam following, and(b) generation, as shown in the Bayer U.S. Pat. No. 2,870,578. Mostmachines used in the prior art make use of a master cam whose surface isreproduced on the workpiece. For instance, the patents of Davies U.S.Pat. No. 2,42l,548, of Appleton U.S. Pat. No. 3,259,021, and that ofHoglund U.S. Pat. No. 3,663,! 88 show such machines in which the shapeof the finished workpiece is dictated by the shape of a master cam. Thedriving action for moving the workpiece rotatably relative to thegrinding wheel, has been introduced through the cam follower to the camsurface. The difficulty with such constructions is that, first of all,the amount of friction that is available between a cam follower and amaster cam is limited, which means that large amounts of metal removalare not possible. Furthermore, tremendous wear takes place between thecam follower and the cam surface, largely due to the amount of powertransmitted through these surfaces. In other words, the larger amount ofpower that is transmitted (enabling the removal of large amounts ofstock), the greater the wear between the surfaces, thus introducingerror beyond allowable tolerance. Another limitation that has beenintroduced into the prior art machines. is the problem of maintainingnormalcy between the grinding wheel and the surface to be finished. Lackof normalcy introduces variations in grinding force, the vector ofgrinding force, variations in relative speed between the grinding wheeland the workpiece. and the like, all introducing errors of variousmagnitudes into the finished surface. The only way to avoid such errors(or at least maintain them below a predetermined tolerance), is to grindvery slowly with small forces. Since such a grinding machine is a ratherlarge capital investment, the long grinding cycle makes the workpieceexpensive and tends to eliminate it economically from being competitivein the market place. These and other difficulties experienced with theprior art devices have been obviated in a novel manner by the presentinvention.

It is, therefore, an outstanding object of the invention to provide agrinding machine for generating an epitrochoidal surface which permitsthe introduction of large amounts of power without at the same timeintroducing error into the shape of the finished surface.

Another object of this invention is the provision of a grinding machinefor generating an internal epitrochoidal surface which permits theremoval oflarge amounts of stock in a unit time and,thercfore, permitsshort grinding-cycle times.

A further object of the present invention is the provision of a grindingmachine for producing an epitrochoid in which a high capital expenditurefor the machine is justified by the fact that the amount of such expensewhich needs to be applied to each workpiece for the process ofgenerating the surface is small.

It is another object of the instant invention to provide a grindingmachine for the generation of an epitrochoidal surface which is made upof relatively simple rugged parts, permitting operations for longperiods of time without shutdown for maintenance or repair; theparameters of the epitrochoid (R R and E) are adjustable and do notrequire different rolling contact elements for each engine size andshape variation.

A still further object of the invention is the provision of a grindingmachine for generating an epitrochoid, which machine is simple tooperate with the use of relatively unskilled labor.

Another object of the invention is the provision of a grinding machinefor non-circular internal surfaces, wherein a shape and normalcygenerating elements are confined in one area; more specifically, theseelements are confined to the workhead and no motions are transmitted tothe wheelhead.

With these and other objects in view, as will be apparent to thoseskilled in the art, the invention resides in the combination of partsset forth in the specification and covered by the claims appendedhereto.

SUMMARY OF THE INVENTION In general, the invention consists of agrinding machine for generating an epitrochoidal surface having a base,having a column extending upwardly for the base, and having a wheelheadmounted on the column, the wheelhead including a vertical spindle on thelower end of which is mounted an abrasive wheel. Means is provided formoving the wheelhead relative to the column selectively in a verticaland a horizontal direction and a workhead is mounted on the lbasecapable of holding a workpiece on which the said surface is to begenerated by the abrasive wheel or other cutting tool. The workheadmoves the workpiece horizontally relative to the spindle to produce anepitrochoidal pattern.

The workhead includes a table mounted on the base for sliding motion ina first horizontal feed direction normal to the trochoid surface, aworkpiece platen mounted on the-upper part of the table for rotationrelative thereto about a vertical major axis, l, and a shaft mounted onthe lower part of the table for rotation about a minor axis, II. Thelower end of the shaft is formed'with a cylindrical stub which isrotatably carried in a hydrostatic bushing mounted on the base, the axisof the said cylindrical stub being displaced from the said minor axis.

More specifically, the shaft is formed as an upper part which isrotatably carried in the table and a lower part which has thecylindrical stub. The upper and lower parts are slidably joined forlateral movement to adjust the amount, E, by which the stub axis isdisplaced from the minor axis.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention,however, may be best FIG. 4 is a diagrammatic representation of themethod by which anepitrochoid-is generated.

FIG. 5 is a vertical sectional view of the machine taken on the line V-VofFIG. 2.,

FIG. 6 is a vertical sectional view taken on the line VI-VI of FIG. 5,

FIG. 7 is a plan view of a portion of the machine as viewed along theline VII--V-II of FIG. 5. i

FIG. 8 is a vertical sectional view. taken on the line VIIIVIII of FIG.7,

FIG. 9 is an end elevational view machine shown in FIG. 7,

FIG. 10 is a plan view ofa portion of the machine as viewed along theline X-X of FIG. 5,

FIG. 11 is an end elevational view of the portion of the machine shownin FIG. 10, p

FIG. 12 is a plan view of a portion of the machine as viewed along theline XIIXII of FIG. .6,

FIG. 13 is an end view of the portion of the apparatus shown in FIG. 12,I

FIG. 14 is a horizontal sectional view of the machine taken on the lineXIV-XIV of FIG. 5, I

FIG. 15 is a plan view of a portion of the machine,

FIG. 16 is a vertical endelevational view ofthe portion of the machineshown in FIG. 15,

FIG. 17 is a vertical sectional view taken on the line XVIIX\ /II ofFIG. 15,

FIG. 18 is a vertical sectional view taken on the line XVIII-X\ III ofFIG. 15,

FIG. 19 is a vertical sectional view taken on the line XIXXIX of FIG.15, I I I I FIG. 20 is a vertical sectional view taken on the line XX-XXof FIG. 15, and v FIG. 21 is an elevational view of a portion of theapparatus shown in FIG. 15. l

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and2, which best show the general features of theinvention, the grindingmachine, indicated generally by the reference 'numeral 10, is shown ashaving a base 11 from one side of which extends a vertical hollow column12. A wheelhead 13 is mounted on a feed slide 1614 and a vertical slide16. It includes a vertical spindle 14 on the lower end of which ismounted an abrasive wheel 15. A cylinder 16b is provided for moving thewheelhead l3 vertically relative of the portion of the FIG. 5 shows asectional view through the table 23' with the workhead l8 suitablymounted for rotation in roller bearings 36 and having a worm gear 37mounted on its lower end for'producing the rotation. Mounted at the topof the workhead is a cam 38 which engages a cam follower 39 mounted onan arm 41 which is fastened to the base 11 throughan abutment 42 (seeFIG.

2). The cam 38 is used when appropriate to give the ultimate shape ofthe finished surface. The cam can be shaped by grinding it in thepresent machine just as though it were a workpiece. The cam may havechanges or corrections to the true epitrochoidal shape to compensate forthermal distortion of the housing during the operation of the engine orto compensate for grinding wheel force variations due to the presence ofan exhaust port acting as an interruption of the surface.

These variations are provided by employing a control systemincorporating a stepping motor, not shown.

The table 23 is formed of four major parts. a bottom part 43 that isfastened to the base 11, a second part 44, a third part 45, and a toppart 46 in which the workhead 18 is mounted. The second part 44 and thethird part 45 are slidable relative to one another for adjustment, whilethe third part 45'and the top part 46 are similarly adjustable, thesebeing in a transverse plane;

i.e., transversely of the grinding machine 10 and in the plane of thedrawing of FIG. 2. The third part 45 is I formed in two parts which arerotated relative to one another by means of a large diameter rollerbearing 47. Extending between the second part 44 and the bottom part 43is a shaft 48. This shaft consists of an upper part 49 and a lower part51 which are slidable relative to one another in the plane of FIG. 5 bymeans of interengaging ways 52 and 53 and locked in that position ofadjustment by a bolt 54. The lower part 51 of the shaft 48 is providedwith a cylindrical portion 55. which resides in a bore in aring 56 whichis attached to an abutment extending upwardly from the bottom part 43 byto the column 12, while a steeping motor 17 is provided in a generallyepitrochoid pattern in a manner which will be described more fullyhereinafter in connection with the description of the table 23 which ismounted on the base 11 and which carries the workhead 18.

The front surface of the column 12 is provided with ways 24 on which aplate 25 is vertically slidable. The wheelhead l3 and its associatedequipment are mounted on this plate. The plate is suspended from cables26 which pass over pulleys 27 and 28 mounted at the top of the column12, the other end of the cable being attached to a weight 29 located inthe interior of the column.

means of reed plates 57 and 58. The reed plates 57 and 58 permit thering 56 a degree of resilient normal motion .in a horizontal plane whenthe cam 38 is used to control the grinding. When generating, however,suitable stops are provided to lock the ring. The shaft 48 also has itsupper part 49 carried in bearings 59 and 61 and it is provided with aworm gear 62 by which it-is rotatably driven about the axis defined bythese two bearmgs.

Spaced from the shaft 48 is a secondary shaft 63, rotatably carried inthe second part 44 of the table by means of roller bearings 64 and 65.It also is provided with a worm gear 66 by which it is rotated in thesebearings. The lower end of the shaft 63 is provided with adownwardly-extending cam follower 67 which is suitably carried in apassage between two guides 68 as will be described more fullyhereinafter.

Mounted in the second part 44 is a motor 69 whose output shaft carries agear 7'1. This gear engages a gear 72 which, in turn, engages a gear 73.The gear 73 drives a shaft and worm which. in turn. drives the worm gear37, while the gear 72 drives another worm which en gages the worm gears62 and 66, aswillbe described more fully hereinafter. 51 r FIG. 6 showsparticularly well the way in which the various partsof the table 23 areslidably mounted on one another. As isevident in the'drawing, the bottomportion 43 issecurely bolted to the base 11 by means of bolts 74. Itshows particularly well the construction of the ways 52 and 53 thatpermit adjustment between the upper part 49 and the lower part 51 of theshaft 48. The third part 45 of the table is slidably mounted on'thesecond part 44 by means of the ways 75 and 76. It might besaid that thesecond part 44 is suspended from the third part 45 and hangs downwardlyfrom it.In the same manner the third part 45 is suspended from its outerportion 77 by means of the bearings 47. The other portion 77 rests onupwardly-extending abutments of the bottom part 43. For instance, in therighthand side in the drawing (at the front in the grinding machine) thebottom part 43 is provided with an upwardly-directed abutment 78 havinga flat upper sur face 79 on which the outer portion 77 slidably rests.At the other side the bottom part 43 is provided with anupwardly-directed abutment 81 having an upwardlydirected V-way 82 inwhich rests a similarly configured way 83 extending downwardly from theouter portion 77 of the third part 45.

In FIGS. 7, 8, and 9 are shown the details of the cam follower 39 on itsarm 41. The arm 41 is of dove-tail construction and is slidably engagedin dovetail ways 84 and 85 on top of the abutment 42. Its position isadjustable by means of a screw 86 threaded into the body of the abutmentand having a head engaging a plate 87 extending downwardly from theoutboard end of the arm 41.

FIGS. and 11 show the details of the top part 46 of the table 23 andshowing the workhead 18 in place. First of all. the top part 46 isdivided into relatively adjustable parts 88 and 89 of which only part 89is shown in FIG. 11. The manner in which 88 and 89 are adjustablerelative to one another is best shown in FIG. 6. The lower part 89 isdisc-shaped and carries the bearings 36, the gear 37. and of course, theworkhead 18. The upper part 88 is provided with slots 91 and fasteningbolts 92. In addition, a peg 93 extends downwardly from the upper part88 into a groove 94 formed on the upper surface of the lower part 89 atone side of the parts. At the other side a similar peg 95 slides in agroove 96. Parts 88 and 89 fit together to form the upper part 46 of thetable. which is rotatably carried in the bearings 47 which. in turn. arecarried by the third part of the table. This third part is shown in FIG.11 and shows at one side its V-way 83 and on the other side the flat way97, which is slidablc on the surface 79,

of the abutments 78 of the bottom part 43 of the table.

Suitable oil passages 98 and 99 are associated with the ways 83 and 97.respectively, to provide them with bydrostatic oil. FIG. 10 also showsthe manner in which the gear 73 operates a worm 101 to drive the gear 37at the bottom of the workhead 18.

FIGS. 12 and 13 show the detailsof the second part 44 of the tablewhich, it will be recalled. is suspended from the top part 46 by meansof the ways 75 and 76. For that purpose, the secondpart 44 is providedwith dovetails 102 and 103 along with a= gibl'04. Extending through thepart 44 is a shaft 105, 'on oneend of which is mounted the gear 72operating worms 106 and I07 which engage-and drive the worm gears 62 and66, re spectively. The latter gears are, of :course, associated with theshaft 48 andthe shaft 63, respectively. The shaft is suitably mounted inbearings and the end plate 108 is shown in FIG; 13 as holding the entireassembly together. i 1

FIG. 14 shows the details of the bottom part 43 of the table 23. Itshows the manner in which the block 56 retains the cylindrical portion55 of the lower part 51 of the shaft 48. As is clearly-indi.cated, theblock 56 is supported by leaf or reed plates 57 and 58 whose other endsare connected to abutments 109 fastened to the bottom surface of thepart 43. Suitable stops are provided selectively to limit (or to preventaltogether) the swinging motion of the block 56 on the resilient supportprovided by the-reed plates. Also clearly shown are the parallel spacedguides 68 which retain and guide the cam follower 67 associated with theshaft'63. At one side of the part 43 is the abutment 78 at the upperpart of which are'provided the flat'surfaces 79 for supporting the padsor ways 97 associated with the outer portion 77 of the part 45. At theother side is the abutment 81 which carries the V-way which supports andguides the way 83 also associated with the part 45.

' FIGS. 15-21 show the details of the part 45 and the manner in whichprecautions have been taken to protect the interior of the table 23 fromdust, dirt, and other by-products of the grinding operation. It iscentrally provided with a large bore 111 with recesses above and belowit for carrying the bearings 47. The details of this construction areshown in FIG. 17 where the recesses for the bearings 47 are indicated bythe reference numerals 112 and 113. FIG. 18 shows the V.-way 83, whileFIG. 19 shows the pad 97.

i The operation of the grinding machine 10 will now be readilyunderstood in view of the above description. First of all, the grindingmachine 10,-shown in FIGS. 1 and 2, is operated in a more or lessconventional manner. The abrasive wheel 15 on its spindle 14 is rotatedin the wheelhead13 by means of the motor 20 which is of the twin-screwhydraulic type. It is moved axially along with-the plate 25 undertheimpetus of the cylinder 16. The weight of the plate, wheelhead, etc, istaken up by the cables 23 operating over the pulleys 27 and28 and by useof the weight 29. Oscillatory motion of the abrasive wheel whileoperating against theworkpiece surface takes place .by means of theeccentric 34 operatedby the motor 35. In-feed motion of the abrasivewheel 15 takes place by means of the stepping motor 17, operating on thecross slide l6a forming part of the plate 25. Dressing takesplace bymeans of the dressing apparatus 31 which is selectively moved in and outof operative position by means of the gear 33 reacting with the rack 32.The normal feeding movement of the abrasive wheel 15 transversely of itsaxis is brought about by the stepping motor 17. All of these motionsthat have been described above are those that would be used in grindingan internal cylinder. Further motions are introduced by means of thetable 23 to produce a non-circular shape in the workpiece to produce theepitrochoidal surface 22.

. With particular reference to FIGS. 5 and 6, there are two types ofmotions that take place in the table 23. First of all, there are thesliding and rotating motions which take place in every cycle in order tocause the abrasive wheel to form the proper surface in the workpiece.Secondly, there are the adjustments that can be made in the parts toproduce the proper geometric relationship between the parts during aninitial adjustment. FIG. 3 shows the manner in which variouscompensatory movements are added to the generation of the truetheoretical epitrochoid in order to produce the desired shape and theseare produced by continuous sliding variations introduced in variousways. The third part 45 of the table slides on the bottom part 43 in theplane of FIG. 5, while the rest of the table including the top part 46and the second part 44, as well as the workhead l8, rotate inside of thethird part 45 due to the presence of the large roller bearing 47. Inother words, the workpiece which has been fastened to the workhead I8 issubjected to sliding motion due to the sliding between the part 45 andpart 43 and to rotating motion or swinging motion due to its presence inthe bearing 47.

The other type of motion, which is for adjustment, takes care of theproblem of generating an epitrochoid 'as shown in FIG. 4. These aretaken care of by the sliding motion between the upper part 49 and thelower part 51 of the shaft 48 whereby the eccentricity E is adjusted.The radius of the major or base circle R is adjusted by the adjustablesliding motion between the two parts 88 and 89 of the part 46 of thetable. The radius R of the minor circle is determined by the adjustedrelationship between the second part 44 and the part 45 from which it isdependent; this adjustment takes place by virtue of the ways 75 and 76engaging the dovetails 102 and 103, respectively.

Referring again to FIG. 5, the operation of the motor 69, operatesthrough the gears 71, 72, and 73 to operate the worms 101, 106, 107which, in turn, serve to operate the worm gears 37, 62, and 66.Understanding the operation of the table motion is easier if oneunderstands that the shaft 63 and its rotation combine with theengagement of the cam follower 67 with the guide 68 only to reinforcethe swinging motion of the part 46 about the main bearings 47 inaddition to the swinging motion introduced by the main shaft 48. Therotation of the shaft 48 (which acts as a crank when E is other thanzero) causes the entire upper part 46 of the table to slide along theways 79 and 82. The sliding motion is purely longitudinal and moves theworkpiece toward and away from the grinding wheel axis in a straightline. Of course, at the same time that this motion is taking place, theworkhead 18 is being rotated. The upper part 46 is being swung about themajor axis presented by the bearings 47, so that the swinging actiontakes place in a harmonic manner. This is reinforced by the engagementof the cam follower with the guide 68 as the shaft 63 is being rotated.This causes the grinding wheel to maintain normalcy with the surfacewhich it is grinding. The introduction of the cam 38 into the situationmeans that an over-ride movement is provided in the longitudinaldirection, that is to say, movement of the entire upper part 46 alongthe ways 79 and 82. This cam serves only the purpose of varying theshape of the epitrochoid slightly away from the theoretical shape toconform to manufacturers specifications. This may be necessary frompractical considerations to provide better operation of the Wankelengine rotor within the housing chamber. An examination of FIG. 3 showsthat the true epitrochoid is generated because of the fact that theworkpiece is being rotated about the axis of the workhead 18 (as definedby the bearings 36), while at the same time, it is being movedlongitudinally by the crank provided by the shaft 48. Next, thecompensation for non-normality takes place by the swinging action of theupper part 46 about the major axis of the bearings 47 due to theoperation ofthe shaft 48 and the shaft 63. The shape can be varied, inaccordance with manufacturers specifications, due to the shape of thecam 38 and its engagement with the cam follower 39. The cam 38 isallowed to over-ride the motion due to the shaft 48 because of the factthat the block 56, which carries the cylindrical portion 55 of the lowerportion of the shaft 48, is mounted in the resilient reed plates 57 and58 (and these plates are released from their stops), so that the camaction tends to move the whole upper part 46 of the table backwardly inaccordance with the shape of the cam. Finally, after all of thesemotions have been taken into consideration, the desired shape of theworkpiece surface 22 is obtained.

Referring to FIG. 4, it can be seen that the true epitrochoid isobtained by the trace or locus of a point P as the minor circle rotatesaround the base circle. In the present machine the radius R, of the basecircle is determined by adjustment of the two parts 88 and 89 of theupper part 46 of the table. This has the effect of changing the distancebetween the center line of the bearing 47 and the center line of theworkhead bearing 36. The size of the radius R of the minor circle can beadjusted by means of the adjustment between the portions 44 and 45 ofthe table indicated in FIG. 5. It will be recalled that the portion 44is suspended from the inner part of the portion 45 by means of the waysand 76 on the one hand and the ways 102 and 103 on the other hand (as isseen in FIG. 6). Finally, of course, the eccentricity E can be changedby the ad justment possible between the upper and lower parts of theshaft 48. Adjustment of the portion 44 relative to the body 45, ofcourse, changes the distance between the axis of the large bearing 47and the axis of the hearing 59 in which the upper part of the shaft 48is carried, while the adjustments between the upper and lower parts ofthe shaft 48 change the distance between the axis of the bearing 59 andthe axis of the bearing provided by the ring 56 in which the lowerportion 55 of the shaft 48 is carried. This, of course, has the effectof changing the amount of reciprocation of all of the upper parts 44,45, and 46 of the table relative to the bottom part 43. Because of theratio of the gearing, the epitrochoid is formed with two lobes.Naturally, if the ratio of the gearing were changed to three-to-one, athree-lobe element would be obtained. When the present apparatus isused, if the eccentricity E is reduced to zero, it can be understoodthat the grinding wheel will generate a cylinder having a radius R plusR If, on the other hand, the eccentricity is changed so that E equals Rthen a cycloidal figure will be obtained which is tangential to themajor circle at one point and is spaced from the major circle by thedistance 2 R at a point from the tangent point. The intermediateposition, where E is less than R gives the epicycloid form that isdesirable in use with the Wankel housing.

One of the outstanding features of the present invention is that it ispossible to adjust R and R to provide a desired workpiece surface. Thismeans that the large cost of the machine is justified by the fact thatthe purchaser is not limited to a given set of epicycloidal dimensions.Furthermore, when the ring 56 is allowed to float on the floor of thebottom portion 43 of the table (by removing the stops which otherwiseengage the ring and the reed plates 57 and 58), it is possible to bringthe cam 38 into operation to determine the shape of the finished circle.Under these conditions in which manufacturers specifications orvariations from the perfect epicycloidal form are introduced, it can beseen that the major portion of power for stock removal is stillintroduced through the main drive portions of the grinding machine. Thisis not affected by the fact that a smaller amount of additional movementis introduced by the cam 38. Since all of the driving power isintroduced into the workpiece through the gearing and the shape of thesurface is determined by the bearings and other elements which carryn'oneof the power introduction. the wearing of such power transmissiongears does not affect the shape of the finished surface. It is possible,therefore, to use very high rates of stock removal. The problem of powerintroduction into the grinding cycle is an important one because mostWankel engines are plated with a very hard material before the finishedsurface is ground into it. This means that the grinding operation whichis performed on the present invention is performed under the mostadverse conditions. That is to say. not only is it desirable to removeas much stock as possible in a given time, but the stock that must beremoved is of a very difficult nature to grind.

There are two basic principles being employed for machining theepitrochoidal surface in a Wankel engine. (a) cam following, and (b)generation. The subject invention deals with a machine that is uniquelyarranged so that it can do both. Both principles have advantages anddrawbacks. Cam copying has the advantage of accurate part-to-partduplication if the cam surface and follower interface stiffness can bemade high enough (straight interface providing normalcy and contact overlong contact line). However, the cam has to be made on another machineand corrections added by trial and error to compensate for errors due tomachine dynamics. With a generator, especially of the type of thepresent invention, with prototype parts the engine parameters R". R andE can be adjusted and varied to machine housing with die-cast models orcams without requiring costly cams for other machines. When using thesubject machine for cam following, the generator is used to maintainnormalcy of wheel feed location and cam follower to trochoidal surfaceand, by means of a resilient member, to preload the cam and follower.One precision generator may be used to make the cam for many productionmachines and'the machines using cams would have a less accurate and lessexpensive generator to maintain normalcy and preload (the radialprecision comes from the cam).

Because of the nature of the present construction. it is possible tobuild the grinding machine very ruggedly, so that the use of highstock-removal rates do not result in deflection of the grinding machineof such a nature as to decrease its accuracy in forming the desiredsurface, nor are there elements which wear sufficiently to introduceinaccuracy into the grinding operation. In the past, because of thelimited power that it was possible to introduce into the workpiece. itwas necessary to grind the surface with several passes of light stockremoval. Because of the many grinding parameters entering the situation.it required highly skilled labor in order to perform this operation,particularly since the plating with the hard material results in a roughsurface. Since the use of the present machine allows the grinding toreach finish size with a maximum of feed rate and extremely largegrinding forces, the desired surface "can be reached within tolerance bya person having only moderate skill in the operation of a grind- 5 ingmachine.

It is obvious that minor changes may be made in the form andconstruction of the invention without departing from the material spiritthereof. It is not, however, desired to confine the invention to theexact form herein shown and described, but it is desired to include allsuch as properly come with the scope claimed.

The invention having been thus described, what is claimed as new anddesired to secure by Letters Patent is: I

l. A machine tool for generating an epitrochoidal surface, comprising a.a base,

b. a column extending upwardly from the base,

c. a toolhead mounted on the column and including a vertical spindle onthe lower end of which is mounted a tool,

d. means for moving the toolhead relative to the column in a verticaland a horizontal direction,

e. a workhead mounted on the base and capable of holding a workpiece onwhich the said surface is to be generated by the tool, the workheadmoving the workpiece horizontally relative to the spindle in anepitrochoidal pattern, the workhead including:

1. a table mounted on the base for sliding motion in a first horizontaldirection,

2. a workpiece platen mounted on the upper part of the table forrotation relative thereto about a vertical major axis,

3. a shaft mounted on the lower part of the table for rotation about aminor axis, the lower end of the shaft being formed with a cylindricalstub which is rotatably carried in a bushing mounted on the base, theaxis of the said cylindrical stub being displaced from the said minoraxis, and

f. a cam means mounted on the workpiece platen for overriding, onoccasion, the sliding motion of the table produced by the said shaft.

2. A machine tool as recited in claim 1, wherein the shaft is formed asan upper part which is rotatably carried in the table and a lower partwhich has the cylindrical stub, the upper and lower parts being slidablyjoined for lateral movement to adjust the amount by which the stub axisis displaced from the minor axis.

3. A machine tool as recited] in claim 1, wherein the table is formed asan upper part which carries the platen and a lower part which carriesthe shaft, the upper and lower parts being slidably engaged foradjustment of the distance between the major axis and the minor axis.

4. A machine tool as recited. in claim 3, wherein the table is providedwith an intermediate part having an upper portion slidably engaging theupper part of the table for relative adjustment therebetween and havinga lower portion slidably engaging the lower part of the table forrelative adjustment therebetween.

5. A machine tool as recited in claim 4, wherein the intermediate partof the table is rotatably mounted in a bearing ring which, in turn, isslidably mounted on the base for movement in the said first direction.

6. A machine tool as recited in claim 5, wherein a motor is mounted onthe table for causing the rotation of the shaft end of the platen.

7. A machine tool for generating a surface similar to an epitroehoid ona workpiece by means ofa tool, comprising: I Z,

a. a bottom part, b. an intermediate part slidably mounted on the bottompart for movement in a straight line, c. a top part mounted on theintermediate part for rotation relative thereto about a first axis, d. aworkhead for carrying the workpiece mounted I on the top part forrotation relative thereto about.

a second axis parallel to and spaced from the said first axis,

e. a shaft having an upper part journaled in the top part and a lowerpart journaled in the bottom part, the axes of the upper and lower partsbeing spaced

1. A machine tool for generating an epitrochoidal surface, comprising a.a base, b. a column extending upwardly from the base, c. a toolheadmounted on the column and including a vertical spindle on the lower endof which is mounted a tool, d. means for moving the toolhead relative tothe column in a vertical and a horizontal direction, e. a workheadmounted on the base and capable of holding a workpiece on which the saidsurface is to be generated by the tool, the workhead moving theworkpiece horizontally relative to the spindle in an epitrochoidalpattern, the workhead including:
 1. a table mounted on the base forsliding motion in a first horizontal direction,
 2. a workpiece platenmounted on the upper part of the table for rotation relative theretoabout a vertical major axis,
 3. a shaft mounted on the lower part of thetable for rotation about a minor axis, the lower end of the shaft beingformed with a cylindrical stub which is rotatably carried in a bushingmounted on the base, the axis of the said cylindrical stub beingdisplaced from the said minor axis, and f. a cam means mounted on theworkpiece platen for overriding, on occasion, the sliding motion of thetable produced by the said shaft.
 2. a workpiece platen mounted on theupper part of the table for rotation relative thereto about a verticalmajor axis,
 2. A machine tool as recited in claim 1, wherein the shaftis formed as an upper part which is rotatably carried in the table and alower part which has the cylindrical stub, the upper and lower partsbeing slidably joined for lateral movement to adjust the amount by whichthe stub axis is displaced from the minor axis.
 3. a shaft mounted onthe lower part of the table for rotation about a minor axis, the lowerend of the shaft being formed with a cylindrical stub which is rotatablycarried in a bushing mounted on the base, the axis of the saidcylindrical stub being displaced from the said minor axis, and f. a cammeans mounted on the workpiece platen for overriding, on occasion, thesliding motion of the table produced by the said shaft.
 3. A machinetool as recited in claim 1, wherein the table is formed as an upper partwhich carries the platen and a lower part which carries the shaft, theupper and lower parts being slidably engaged for adjustment of thedistance between the major axis and the minor axis.
 4. A machine tool asrecited in claim 3, wherein the table is provided with an intermediatepart having an upper portion slidably engaging the upper part of thetable for relative adjustment therebetween and having a lower portionslidably engaging the lower part of the table for relative adjustmenttherebetween.
 5. A machine tool as recited in claim 4, wherein theintermediate part of the table is rotatably mounted in a bearing ringwhich, in turn, is slidably mounted on the base for movement in the saidfirst direction.
 6. A machine tool as recited in claim 5, wherein amotor is mounted on the table for causing the rotation of the shaft endof the platen.
 7. A machine tool for generating a surface similar to anepitrochoid on a workpiece by means of a tool, comprising: a. a bottompart, b. an intermediate part slidably mounted on the bottom part formovement in a straight line, c. a top part mounted on the intermediatepart for rotation relative thereto about a first axis, d. a workhead forcarrying the workpiece mounted on the top part for rotation relativethereto about a second axis parallel to and spaced from the said firstaxis, e. a shaft having an upper part journaled in the top part and alower part journaled in the bottom part, the axes of the upper and lowerparts being spaced from each other and parallel to the first and secondaxes, f. a motor producing rotation of the shaft and of the workhead,and g. a drive producing eccentric movement of the top part about thesaid first axis to maintain normalcy between the tool and the workpiecesurface, the top part being formed in two slidably-connected parts foradjustment of the distance from the first axis to the axis of the upperpart of the shaft, the upper and lower parts of the shaft being slidablyconnected for adjustment of the distance between their axes.